The present invention relates to an ultrasonic diagnosing apparatus adapted to diagnosing the diseases of mammary glands and mastocarcinoma.
When ultrasonic waves are applied to a patient, they are reflected by the boundaries between different tissues of the patient. A sectional slice image of an internal organ or abnormal tissue of the patient can be formed from the echoes of the ultrasonic waves. In order to prevent attenuation and reflection of the ultrasonic waves travelling between the patient and a probe which generates and detects the ultrasonic waves, an acoustic coupler is interposed between the probe and the patient. For the acoustic coupler, water is often used because it resembles the patient in ultrasonic-wave propagation characteristics.
FIG. 1 shows a prior art ultrasonic diagnosing apparatus with a receptacle filled with water. A receptacle 10 contains water 2. A patient is held with her breast 4 fitted in an opening 12 of the receptacle 10. A probe 14 is disposed in the receptacle 10 and can be movable in the direction of arrow 6. The probe 14 extends in the direction of arrow 8 (see FIG. 3) perpendicular to the direction of the arrow 6. It has a number of piezoelectric elements 16 arranged in the direction of arrow 8. The elements 16 emit ultrasonic waves toward a region 18 schematically shown in FIG. 3, thereby achieving electronic scanning in the direction of arrow 8. At the same time, the probe 14 moves in the direction of arrow 6, thus performing mechanical scanning. Since the patient's breast 4 directly contacts the water 2, the reflection and attenuation of ultrasonic waves are limited, which results in relatively good sectional slice images. In this prior art apparatus, however, the breast 4 may get wet and foreign matter is liable to enter the water 2. The foreign matter reflects the ultrasonic waves, lowering the image quality. As the patient breathes, her breast moves. This makes it difficult to form an accurate image.
FIG. 2 shows another prior art ultrasonic diagnosing apparatus. This apparatus differs from the apparatus shown in FIG. 1 in that the opening 22 of the receptacle 10 is closed by a membrane 24. The membrane 24 is formed of flexible material having acoustic characteristics similar to those of an organism and can closely contact with the breast 4. The receptacle 10 and the membrane 24 form a vessel. This vessel is filled with water. The breast 4 can be supported by the membrane 24. The depth to which a patient's breast 4 may sink is limited within a range as taken from the ultrasonic probe 14. Thus, the breast 4 is kept relatively flat, pressed onto the membrane 24. Accordingly, when the ultrasonic waves are applied to the breast 4, the direction of incidence of the ultrasonic waves and the surface of the breast 4 define a substantially right angle (incidence angle). As a result, the breast 4 reflects less waves, leading to improved sensitivity, reduced artifacts, and increased depth of visual field.
As shown in FIG. 3, the ultrasonic propagation region, i.e., a specified zone S is narrow since the waves generated by the piezoelectric elements 16 have both a convergent acoustic field and a diffuse acoustic field, whose envelopes have the shape shown in FIG. 3. An ultrasonic diagnosis should preferably be made by using the zone S which is high in ultrasonic density.
Women, as well as men, have breasts of different sizes. Hence, the bottom portion of the breast varies according to the patient although the breast is supported by the membrane 24. The zone S is relatively short in length. Use of a mechanism for adjusting the vertical position of the probe 14 contradicts the requirement for the miniaturization of the ultrasonic diagnosing apparatus. Also, it is very difficult to change the focus point by replacing an acoustic lens in an ultrasonic vibration surface of the probe 14, since the probe 14 is contained in the sealed vessel. Therefore, the region of the breast 4 to be examined by ultrasonic diagnosis may sometimes be off the preferable zone S for the diagnosis. In diagnosing mastocarcinoma, the objective region to be examined is located on that portion of the breast beside the armpit. In this region, however, the contact between the membrane and the breast is loose, so that an air layer is liable to lie between them. Such an air layer makes the ultrasonic diagnosis difficult.
These drawbacks of the prior art ultrasonic diagnosing apparatus are fatal especially in, for example, a group examination in which a number of objects are examined without leaving any substantial chance of reexamination.